In a conventional disc control apparatus for controlling a reading and/or recording head (simply called "head" hereinafter) to access to a disc having a spiral track, the head is controlled to move from a first track (physical) position presently traced on the spiral track to a second track(physical) position to be next traced on the spiral track. In the control of moving the head on the disc having the spiral track, the number of tracks is calculated between the first track position and the second track position, so that the head is moved in an inner or outer radial direction on the disc by a distance determined based on the calculated track number. Operation of moving the head on the disc from the first track position to the second track position at a predetermined high speed is defined as "seek", and a time period which it takes the head to begin reading information stored in the second track position of the disc stably after the head arrives on the second track position is defined as "settling time".
Here, it is assumed that a rotating number of a disc having a spiral track used as, for instance, a CD-ROM is 360 rpm, and a moving speed of a head is 3 msec/one track, and further assumed that information is read from the center portion of the disc to the peripheral portion thereof under a state that the disc is rotated such that a track speed is linearly maintained constant relative to the head. Where the head is controlled to move from a first track position A of a spiral track to a second track position B of the spiral track which is on the outside relative to the first track position A by the track number of 5, the head is started to move in a direction from the first track position A to the outer peripheral portion of the disc, and is stopped to move when the number of tracks is counted by "5", so that the head is assumed to arrive on the second track position B. Accordingly, information is read from the first track position A of the disc and then the second track position B of the disc successively.
According to the conventional disc control apparatus, however, there is a disadvantage that an access time becomes long for the following reason. That is, the disc is kept rotating during the moving of the head in the radial direction on the disc, thereby resulting that the head is positioned to be deviated from the second track position B which is a destination of the head by a distance determined based on a product of a moving time of the head and a rotating speed of the disc. As a result, operation of correcting the deviated position error in which the head is corrected to move from the deviated position to the destination (the second track position B) is necessary to be carried out.
In accordance with the aforementioned assumption, the rotating number N.sub.R1 of the disc is calculated during a time period of moving the head from the first track position A to second track position B in the equation (1). EQU N.sub.R1 =360 rpm .times. 3 msec/one track .times. 5 tracks=0.9(1)
The rotating number N.sub.R2 of the disc is calculated during a settling time in the equation (2), where the settling time is 1.5 msec. EQU N.sub.R2 =360 rpm .times. 1.5 msec=0.09 (2)
Consequently, the total rotating number N.sub.R of the disc is calculated in the equation (3). EQU N.sub.R =N.sub.R1 +N.sub.R2 =0.9+0.09=0.99.apprxeq.1 (3)
That is, the disc is rotated by approximately one before the head is stopped to read information from the disc.
As a result, the head is inevitably moved to a third position C approximately corresponding to a track which is on the outside of the second track position B by one track number, unless the operation of correcting the deviated position error is carried out.